Interfacial Partitioning of a Loop Hinge Residue Contributes to Diacylglycerol Affinity of Conserved Region 1 Domains [Signal Transduction]

August 14th, 2014 by Stewart, M. D., Cole, T. R., Igumenova, T. I.

Conventional and novel isoenzymes of Protein Kinase C (PKCs) are activated by the membrane-embedded second messenger diacylglycerol (DAG) through its interactions with the C1 regulatory domain. The affinity of C1 domains to DAG varies considerably among PKCs. To gain insight into the origin of differential DAG affinities, we conducted high-resolution NMR studies of C1B domain from PKCδ (C1Bδ) and its W252Y variant. The W252Y mutation was previously shown to render C1Bδ less responsive to DAG (Dries et al. (2007) J. Biol. Chem. 282, 826-830) and thereby emulate the behavior of C1B domains from conventional PKCs that have a conserved Tyr at the equivalent position. Our data revealed that W252Y mutation did not perturb the conformation of C1Bδ in solution but significantly reduced its propensity to partition into a membrane-mimicking environment in the absence of DAG. Using detergent micelles doped with a paramagnetic lipid, we determined that both the residue identity at position 252 and complexation with diacylglycerol influence the geometry of C1Bδ-micelle interactions. In addition, we identified the C-terminal helix α1 of C1Bδ as an interaction site with the head groups of phosphatidylserine, a known activator of PKCδ. Taken together, our studies (i) reveal the identities of C1Bδ residues involved in interactions with membrane-mimicking environment, DAG, and phosphatidylserine, as well as the affinities associated with each event, and (ii) suggest that the initial ligand-independent membrane recruitment of C1B domains, which is greatly facilitated by the interfacial partitioning of Trp252, is responsible, at least in part, for the differential DAG affinities.